Not so. It will prevent/reduce boioer cycling that is for certain.
Your comprehension is poor. The boiler/heat bank maintain the lowers section of the heat bank at the temperature that the rads require for optimum performance. That is very simple.
This weather compensator is NOT integrated with a boiler. This you can't understand.
Nope.
Yes.
?? One to sense the temp of the heat bank
Uh! Switched? room temp trimming is analogue unless to have a cheapo.
Or boiler flow, which most operate on. Used on the heat bank here.
Could be on the cylinder not far from the boiler/rads returns pipes.
It is clear you do not understand. The rad circuits are off the bottom of the heat bank and have their own pump. Easy. The boilers flow and return is off the heat bank, at the bottom of the heat bank. The compensator has a probe on the bottom section of the heat bank producing a mass of water at the temp the rads require. The lower temp at the bottom on part load will ensure low temp return for high efficient condenser operation, with an expensive complex boiler.
The room temp influence only trims.
No. Get the boiler to heat a mass of water all at one time, to what temperature the room requires.
No need for a modulating condensing boiler./ Most do modulate, but heating boilers modulate on flow setpoint temp. As the boiler will be on full, when heating the mass of water for CH very rare will it modulate.
You still don't understand.
Primary?
And to prevent boiler cycling and giving on-demand mains pressure hot water. Eliminating cold water storage tanks. With a heat bank the DHW and CH circuits don't care about the boiler. The boiler can be controlled more efficiently by having it heat one mass of water very quickly and in one long efficient burn. Taken further it can heat two masses of water at different temperatures. High for DHW and low for CH. Taken further again, the CH mass of water can be at variable temperatures to what the outside weather dictates. When called to heat the CH mass of water it does it in one long burn no matter what temperature the CH water mass is.
But you save a wedge on a 1.5K load compensating boiler and musch simpler.
Not so.
You clearly do not understand. "by definition, than the direct connection of the boiler to the radiators as the manufacturers intend and design.". I am not on about one of theses type of boiler.
In the DHW case where either the water in the heatbank is cold or where the rate of use of heat via the plate heat exchanger massively exceeds the boiler capacity, boiler cycling will obviously not occur. That much is obvious.
In the case where the heatbank is sitting between a modulating boiler and the radiator load, it will screw up the control loop and reduce the efficiency of the boiler, simply because the boiler is unable to monitor the radiator load directly.
If you use a non modulating boiler and control it in some way based on the heatbank temperature, that may be better than a non modulating boiler relying purely on its internal thermostat. However, since the burner is either full on or off, it is a) cycling and b) not operating at the optimum temperature - unless you are talking about a non-condensing boiler as well, of course.
If you use a modulating boiler and attempt to control it in an on/off fashion as an external simple weather compensator will try to do, then the efficiency will be worsened as compared with allowing the boiler to monitor the radiator water temperature directly.
It is very simple, and you have it wrong. There is nothing to be gained with partitioning a heatbank when a gas condensing boiler is the sole source of energy. Further to that there is nothing to be gained by having a heatbank in the radiator part of the load at all in this instance.
Oh good grief.
I am fully aware that this weather compensator is not integrated with the boiler. That is why using this type with this application is completely pointless.
There are three useful applications for weather compensation:
a) An external, simple one of the type you describe, like the BEM5000, which has analogue input sensors and a switched output which cycles the boiler on and off. This is useful wih conventional, especially older and possibly overpowered boilers where the hysteresis of the built in thermostat is large and the boiler has a tendency to cause the room temperature to overshoot; and the thermal characteristics of the house tend to cause the same. This type of device reduces the average radiator temperature by switching the boiler on and off rather than letting its thermostat do the job. It's a crude system and may make an improvement in this environment.
b) An external temperature sensor connected to a modulating, condensing boiler's microprocessor. This type of controller already has analogue inputs from the flow and return temperatures and can control burn rate and even the pump. This additional sensor gives additional data from the environment outside the house which will affect the internal temperature after a time. The boiler can then adjust accordingly as well as maintaining minimum power level and temperature.
It isn't possible to achieve the same levels of control and efficiency using method a) as this.
c) A commercial system, where there is an external energy management system having multiple analogue sensors inside and out, and able to monitor the water temperatures. This type of controller is able to control a boiler or boilers which are able to modulate, but by the use of some kind of digital signal (PWM or coded), or via an analogue control voltage or current (e.g. 4-20mA, 0-10v etc.)
Your proposal is for something that is basically a type a) arrangement, but you are claiming that it is equivalent to or better than type b) or c). This is patent nonsense.
Of course you do. One loop is from boiler to heatbank, the other from heatbank via radiators to room.
take a look at the BEM5000. This is the common weather compensator and is hardly cheap.
It has a switched input for the room thermostat.
Contrast this to the Worcester Bosch Greenstar, which can have a modulating room thermostat as an option for £42.
Er no. The important temperature for condensing efficiency is the boiler return temperature.
For other control applications this is also commonplace because it gives an indication of what the thermal load is doing.
The BEM5000 uses the sensor on the return.
That makes it even worse. The temperature of the cylinder wall is only vaguely related to the return pipes and will have a time lag.
It's clear that I do, and that your scheme gets more an more complicated and less useful/
An extra pump.
?The boilers flow and return
I presume that you mean without an expensive complex boiler.
Do you think that the Greenstar at £725 is expensive? If you take off the £300 or so needed to implement your scheme, plus the poorer long term reliability because of the extra components, you have about £400 to spend. Are you saying that you can get a good quality condensing boiler for this.?
Since the external box weather compensator is going to turn the boiler on and off to maintain the temperature, it will not run at its most efficient. You would be trying to match a (say) 30kW boiler into a (say)
This depends on the thermal characteristics of the building.
This is why your approach is nonsense.
If you were to connect the modulating boiler directly to the radiators, an average flow temperature will be in the 50 degree area.
If you try to do this via part of a heatbank and set that temperature, there is relatively little energy storage - the typical volume of water is perhaps half of the radiator capacity.
Very soon, the water temperature in the heatbank will have fallen and the boiler has to come on again. In effect, you are making it cycle by having regular relatively short full power burns.
This is not as efficient as letting the boiler run continuously at the temperature required for the radiators.
There are very few quality ones that don't.
... and also account for the return temperature.
It will be cycling inefficiently instead.
Not only that, the radiator temperatures will be fluctuating as well.
Fundamentally, you can either let the heatbank cool right down and reheat it at full power which causes the boiler to run less efficiently and radiator temperatures to vary, or you can attempt to maintain a setpoint. If you do the latter, then having the boiler going on and off is not the best way to do it.
I think that you don't or are simply being obtuse.
That is implicit in what I said.
They have totally different characteristics.
The DHW application needs large amounts of heat for relatively short periods of time. That is why it is called a heat *bank*. It allows overdrafts relative to the capabilities of the boiler.
The CH application requires much smaller amounts of heat on a continuous basis with quite slow rates of change of demand.
That is only true for the DHW case. For the CH case it is not. We have already established for a condensing boiler that it will run more efficiently at lower temperatures and power levels continuously than by switching on and off.
For the DHW application, the main purpose of a long burn at high power level is to transfer as much energy as possible back into the cylinder as fast as possible.
So now we have two heatbanks?
The burn and cycle time will vary with the rate of use of energy and the amount of temperature drop allowed before reheating is initiated. This is far from efficient.
Where did you get £1.5k from?
I mentioned the WB Greenstar at £725 with all these features.
Sigh.....
So you mean a non modulating boiler? These are not as efficient as modulating types by definition, and all that you are proposing is to put a simple switching controller and a damping element in front in an attempt to make them so. This is a nonsense.
Nonsense. Thew boiler doesn't need to know the return temp of the rads.
You are getting there.
Failed.
Failed again.
Failed again. When on it heats a large mass of water. This confuses you. That is sad.
Failed again. It is right it is just above.
Lots to be gained. A cheaper simpler boiler and vastly reduced/elimination of cycling.
A heat bank a neutral point. A great advantage. The boiler and rads operate independently of each other. Constant flow can be through the boiler at all times. No silly pressure diif valves needed. Rads with TRVs can be virtually off and the boiler doesn't know or care.
Sounds encouraging.
Failed again.
It is. When using heat bank.
None of your points has a heat bank incorporated, so squewed.
Only one loop. Boiler to heat bank, dictated to by outsoide waether conditions.
It is not the only model. It saves the cost of a 1.5K boiler.
Not good if room influence is incorporated.
Only doe one zone. A heat bank can have two zones fed from it. Each zone hits a neutral point. Microbore can be used when both go back to one neutral point.
Er yes, depending on application.
Lower the flow and the return follows suit.
Using a heat bank the thermal load is irrelevant. The boiler doesn't care about it.
Just an option they use.
failed. makes it better as it sense the mass of water, which is at the temp the building requires.
The boiler doesn't want to know the rads return temperature. I doesn't care.
No. It is clear you do not understand.
It is simple. It also works very well indeed.
That will break the bank.
yep.
Not bad for what it is. Others are cheaper. This is besides the point.
You have a simpler boiler with less components.
failed again.
It doesn't, it depends on what compensator you use.
failed again. See above
Once the buildings heat demand is below the minimum of the boiler cycling starts.
You make sure the storage is at least x 2 of rads.
Getting it.
No. short power burns at lomng intervals.
failed again.
failed again. Not so.
Fluctuation of rad temps would be minimum.
failed again. the boiler runs efficiently. as the mass of water is to the temp the building requires.
failed again.
No. You still don't understand.
Which is a great advantage. Divide and rule.
failed again. It is called a heat bank because it is a bank of heat.
failed again. applicable to CH.
failed again. applicable to CH.
Good. getting better.
Faile again. Continuous power levels when burning in one long efficient burn.
Good.
One split into two separte temperature zones.
Efficient for the boiler usage.
A load compensating modulation, outside waether compensating boioer is about
1K
Using a heat bank load compensating modulation is not required.
Outside weather compensation?
Yes.
failed again. They are. It depends on how it is controlled and what conditions it is run in.
2/10 total failure. And you say O and A levels are getting easier. You just failed.
failed again.
2/10. very poor mark. You should feel ashamed of yourself.
It does if it is going to be involved in an efficient control system where the heat output to the radiators and the heating space are measured and controlled without lag, then it most certainly does.
I said *may*, and it will only be in so far as a difference between an analogue sensor on the cylinder and a thermostat with substantial hysteresis on the boiler.
The whole thing is then wrecked by the external controller driving the boiler in on/off mode.
So are you saying that the external controller doesn't control the boiler by turning it on and off. You'll be telling me that it operates a motor on the gas tap next.
If it is a condensing boiler, on/off control with full output or nothing will not operate it efficiently.
The trouble is that it doesn't.
On the one hand you are saying that you are going to have part of a heatbank operating at a set point and being maintained that way by controlling the heat going in. By definition, if you do that with a non-modulating boiler with power output level larger, probably substantially larger than the rate of use by the radiators, then you will have to cycle the boiler. That is unless you know some law of physics whereby heat can be stored in a different dimension.
On the other hand, you say that you want to have long burns on the boiler to improve efficiency (which it only does by not having cycling, not because of running temperatures). If you do that, you are going to have to let the heatbank (or part thereof in use) discharge all of its heat before running the boiler again. This will result in cooling and heating of the radiators, a fluctuation in heat output and a variation in room temperature.
You can't have it both ways.
As I said, you can't have it both ways.
There's nothing to be gained.
You have added a bunch of complexity and achieved poorer efficiency.
You haven't saved any money either Please provide a make and model number of one of these "simpler boilers" at around £400 Discounted Heating prices, that is anywhere near the quality of a WB Greenstar.
Only in circumstances where
a) multiple heat sources are being combined or
b) when there is a need to store heat because of the requirement of large amounts to heat water, or
c) when the boiler, because of its sizing and limited or no control range would naturally cycle.
This is not any of those cases.
That's clearly nonsense. The only way that they can operate truly independently is by having two heat banks. Are you advocating that now?
The heat requirement into the cylinder will be quite different for DHW vs. CH. In the former case, it will be maximum transfer after water has been run. In the latter, either the heat will have to be fed in at the rate of use (less than the boiler maximum output) or at full power for short periods.
Where you have got the idea of constant flow from, goodness only knows. If you mean constant water flow, regardless of demand, it is going to be wasteful when neither CH nor DHW are demanding heat.
There aren't anyway. If the pump is integral to the boiler, the boiler's controller can match it to the heat load. An exterior one can sense the flow and pressure conditions and also reduce output.
I'm not repeating the obvious, and I'm certainly not about to educate you about control systems.
Not if the controller is operating the boiler by turning it on and off, which it will have to do in the case of a non modulating one. This is how the BEM5000 works. All that the heatbank is doing is to add a lag in the control path.
Again. All that the heatbank does is to introduce a lag in the control system. You can either choose to keep it topped up with heat on a tight setpoint window, in which case the boiler will have to be cycled a lot, or you can let the heatbank temperature drop by the use of a wide window in which case it will cycle less and the radiator temperatures will drop.
There is also the room thermostat or TRVs as an outer loop.
The heatbank is not representative of the characteristics of the radiator heat load. All that you achieve at best is a rather poor attempt at providing a heat source to the radiators, the temperature of which is varied according to outside conditions. THe boiler energy manager, will attempt to maintain the heatbank temperature by cycling the boiler on and off.
There is no value in doing that in comparison with a true modulation of the boiler.
Please provide an example of a suitable weather compensating controller at the same or lower price than the BEM5000.
Please also explain how you believe that on/off controlling a simple boiler is more efficient than a modulating, condensing one.
Please explain where the figure of £1.5k comes into this. The discussion is around something like a WB Greenstar with price point of £725. It's not good trying to justify your argument by adding in £800 of cost which is irrelevant.
THe arithmetic is between a good quality modulating boiler at £725 vs. the cost of some alleged "simple" boiler at £400 plus your controls at £300.
Exactly.
This is irrelevant. The issue is still one of energy in vs. energy out.
This is irrelevant as well. Microbore is simply a size of tube. There is nothing magic about it.
Sigh.....
Well obviously. Most modulating boilers that I have seen have both flow and return sensors.
Oh dear. Of course it's relevant.
THe DHW load is an overdraft on the heatbank of anything up to 200kW for short periods of time. Boiler requirement to recharge is full power, for a short time.
The CH load is likely to be 20-80% of full load according to demand and is continuous during short to medium time periods.
It's pretty critical to the operation of the operation of the unit.
From the instructions:
"The ESMA must be mounted on a pipe connected to the boiler return tapping, between the bypass and the boiler, using the clamping band provided, in a position where it will sense the temperature of the water returning from the HEATING circuit"
ESMA is the return sensor. It doesn't say *may* but *must*.
Regarding the room thermostat it uses the words
"If a room thermostat is used....."
i.e. optional.
The mass of water will be at some temperature. The controller should be trying to measure the radiator return temperature in your example because that represents something derived from the heat load into the space. The temperature of the heatbank is not well related to that.
In the case of your external controller and full power switched boiler set up, obviously not. The closest would be that the controller wants to know the return temperature from the radiators.
However the exercise is pointless because it will be worse than letting a controller in the boiler do the job.
It's behind you.......
Have you implemented and measured this in comparison to a modulating condensing boiler connected to radiators directly?
If so, which boiler and controller did you use for each?
None of this breaks the bank.
The point is that you are proposing an unnecessarily complicated system, which patently can't perform as well as one with analogue sensing of water temperatures and modulation of the burner.
You are unable to provide types and prices of components for this that will come in at under the price point for a modulating system.
Not really. You can get modulating, condensing boilers for a bit less than this, or a bit more.
What is the make and model number of your alleged "simple" boiler, with equivalent build quality to this?
They are all external in various boxes, valves and extra pumps.
No you fail to understand.
The equations are simple.
In the modulating, condensing boiler case, if the load to the radiators needs to be 10kW, the boiler will drop down to that output level and a low running temperature, continuously. There will be no cycling at all and the boiler will be running well into into the higher efficiency part of its operating curve.
In your simple boiler case, the 10kW load match will have to be achieved (assuming a 30kW boiler) by running it at full power for a third of the time. This is less efficient, a) because the boiler is going on and off and b) because it is not operating on the most efficient part of the curve. You can make those on/off periods shorter or longer by how large you make the allowable temperature drop in the heatbank, but it will average to a 3:1 off/on.
Oh really. What kind of compensator do you have in mind?
It is possible to run a modulating boiler purely based on outside temperature measurement, but the effect will be that the inside temperature will tend to fluctuate.
Sigh.
Obviously. However it is far better if it cycles between 0 and 20% of full load than 0 and 100%
So let's see. My radiators and pipework have a capacity of about
100 litres.
So now you are saying that I need a 200 litre heatbank for this; and the one for the hot water in addition to that?
Plus I get worse performance and efficiency than a boiler connected directly to them?
Why would I want to do that?
The energy still has to be put in.
With a 200 litre cylinder that will be about 30 mins on - I wouldn't call that short.
It is also not a practically good example because the heatbank has been run to zero in the intervening time.
Do you have figures which demonstrate that running a condensing boiler at full power with cycling is more efficient than running it on part power continuously?
If your case were more efficient, why do you imagine that the manufacturers of modulating boilers arrange them to drop the power and temperature as the load reduces? Do you imagine that British Gas sponsors them to use more energy??
Not if you run the temperature in the heatbank down.
What do you believe that the operating window of the heatbank should be and why?
So are you saying that you want to maintain the heatbank at close to the setpoint temperature or allow it to fall?
If so, by how much?
That's your best argument so far. It's a pity that it bears no relationship whatever to the subject matter.
This depends on the temperature range that you are going to use.
Are you going to try to maintain the set point or allow the temperature to fall?
It will be more efficient at lower temperatures and power levels. With your proposed simple boiler, this doesn't happen.
With what? Some kind of divider or just relying on stratification?
If it's the latter, you are going to get a big interaction between the performance requirement of the hot water vs. your desired control for the CH part. Since the characteristics are completely different, you will end up with a poor compromise.
Whatever that means, which is not a lot.
You introduced the idea of weather compensation as a means to control the heatbank temperature, just so that you could hook up the radiators to it - a completely pointless exercise.
You can equally argue that with a modulating boiler with a room temperature analogue sensor that outside weather compensation isn't required.
Certainly with your suggested method of on off control it is not going to run at anything like the efficiency of a modulating model using its own temperature sensing.
They are measured by the weather compensator, with any room temp influence to drop the slope if need be.
No lag. A mass of water the temperature required is available.
Thermostat on the boiler is on full, and will rarely cut out on this.
No.
Nope I will not.
You fail to understand condensing boilers, or boilers at all. A boiler will only raise water a certain temperature with a given flowrate through the heat exchanger. The flow through it can be constant, as no TRVs used. If say at x flowrate it raises the water 25C, if the return is 30C only 55C come out of the flow. Way below the boiler stat set to 82C. When the mass of water is heated the boiler stat would have never have cut in to cycle the boiler, so one long efficient burn.
You are rarther silly now.
The boiler does not cycle when re-heating the mass. Operation: heats the mass of water > mass cools -> mass is reheated all at once with "no" boiler cycling -> heat extracted from the water mass by the rad circuit -> mass is reheated all at once with "no" boiler cycling .
You are mad.
Mor failure. You have droped from 2/10 to 1/10.
Any fluctuation would be minimal. the mass of water takes time to cool. It is not like hot water running though a rad circuit return pipe. very little mass and less mass in the whole rad circuit than in the stored water mass by at "least" half as much. The water mass stabilises operation. think hard about that. Ermmm well don't bother.
Failed again.
failed again.
Less complexity, as simple cheaper boiler is used.
No expensive 1.5K bpoioer to be bought.
You have a thing about £400.
It is. Even a modulating boiler cycles when demand is below the minimum kW. With a heat bank, no cycling.
Failed again. The boiler and rads operate independently of each other.
failed again.
failed again. Full power for the re-heat time in one burn.
More failure. Boilers have an optimum flow through the heat exchanger.
Heating boilers don't have them integrated, well most don't.
Heating boilers with minimum control are used.
Be sure, you will not educate me on control systems.
Switches on -> one long bur to setpoint -> switches off. Simple.
failed again. not so.
drop by not much at all.
room stat? no there is not. TRVs are not in the boioere control loop.
It provides a mass of water at the temperaure the rads want. The heat bank doesn't care about the rad heat load, it just provides the mass of water for the rads to use.
more failure
All the big makers make compensators at low prices.
Please read all of this thread again.
biolers with built-in load compensation modulation and waether compensation are well north of 1K
You are making things up.
failed again. It isn't
In and out of what? less energy into the boiler for energy out.
Look up how microbore operates.
Not as far as the boioer is concerned.
compensator
compensator
You should find out the advantage of weather compensation.
It should be the other way round of course. We are not trying to control the weather here, but the temperature in the house. The outside temperature is monitored to provide a correction to the slope.
OK, so you don't understand the meaning of the term "lag" in a control system. There is no point in discussing its influence in that case.
OK, so this means that you are relying on the external weather compensator, which is controlling the boiler by switching.
That's good. I just wanted to be clear on that.
That's a relief.
It seems that I understand rather more than you do.
Correct - actually it's more like maximum temperature.
Obviously the boiler won't be cycling on its internal thermostat, assuming it is set high. It will be being switched by the fact that the rate of heat production will exceed the use by the CH. This cannot be as efficient as running the boiler continuously at the level of the radiator heat load. You are also assuming an ideal (in the engineering sense) heatbank where there is no mixing and churning of the internal water. This will have the effect of raising the temperature sensed by your controller higher than it would otherwise be and reducing the run time. If the return were directly from the radiators there would be much less mixing and the return temperature is therefore much more indicative of the actual real load.
If that is your best reply, then there is no point in discussing the point further.
This is physically impossible. If the heat input from the boiler is greater than the heat use and you are not modulating the boiler output, by definition your controller has to cycle it off and then back on again. This is less efficient than matching the boiler output accurately to the load.
That will depend on how you set the operating window of the heatbank.
It will cool at the rate determined by the use through the radiator circuit.
It simply causes control lag, but I know that you don't understand the concept. I know that you don't know what "mass" means.
Your supposition assumes that the volume of water in the heatbank is twice that of the radiators and pipes. Are you seriously suggesting installing a 200l heat bank just to run the radiators?
It seems that you have,
Plus an extra controller, an extra pump, valves and sensors.
The only person who raised the subject of £1500 or £1000 boilers was you in an attempt to divert attention away from your farcical idea. Sorry, but it won't wash.
You also introduced the idea of an external boiler controller using an outside sensor and applied in a way for which it wasn't designed and controlling a boiler in an inappropriate way. You can't even find one that is suitable for what you think you are trying to do.
I do, because that is the comparison point; not your £1500 figure.
Yes of course it does, but at that point - usually around 4-7kW, it doesn't matter anyway. In practice, this only happens for a very short period anyway.
It is cycling because the controller is switching it off and on, and as part of the normal operation. It *always* does this.
Once again your normal MO when you don't understand something - selectively clip.
It is anyway irrelevant if the flow is continuous through the boiler - there aren't any sensors as there are with a modulating boiler.
So is it two heatbanks or one?
Sigh.... Until the heatbank depletes, the thermostat on the cylinder comes on and the boiler runs again, then goes off because the thermostat is satisfied, ad infinitum. This is cycling.
Which is obviously dependent on the rate of heat production for optimised results and why some modulating boilers also modulate the pump.
You have not only a switched boiler, but one which always runs at full power and with the same flow rate. Three efficiency reducing factors.
The term is semantic, which is why I was careful to say "integral pump".
Believe me, I reached that conclusion a very long time ago!!.
There's little else
It will drop by what you want it to drop by. Either you can maintain the temperature near the set point and the boiler will cycle more frequently, or you can allow a larger drop and the radiator temperatures will drop.
The TRVs are in the second control loop. If you remember, you earlier said that there was only one loop. In fact in your scheme, there are at least three.
You're running round in ever decreasing circles now. Earlier you made a big point about the external weather compensator maintaining an appropriate temperature for the radiators. Now you are saying that it doesn't matter. You can't make up your mind whether you want the heatbank temperature to be maintained or rise and fall dramatically.
In short you are guessing.
es.
I see. Please name some and provide the prices.
You have got to be joking.
This is not the comparison that we are making. The simple solution was of a modulating boiler running the radiators directly. You have added in all the complexity of weather compensators hooked up to external controllers whose purpose is to switch cycle old non-modulating boilers in an attempt to make them a bit more efficient in the system.
Clearly a modulating boiler with an external temperature sensor directly hooked in is going to outperform one without and certainly your scheme. Therefore there is little point in doing a comparison on this basis.
You're looking in the wrong place. You're trying to alter the basis of the discussion to a different price point and different functionality and efficiency.
Stick to the question. Where are these simple £400 good quality boilers?
The heatbank, obviously.
I know full well how microbore operates. It's copper tube. End of story.
Not directly because your boiler has no sensors. Taking the system as a whole, it is highly relevant.
I know the advantages of weather compensation, properly implemented, quite well, thanks. I have such an arrangement, remember. I also have the ability to log precisely what the boiler is doing in terms of burn rate, fan operation, pump operation and 6 different system temperatures.
Then please explain why the boiler manufacturers engineer their products to modulate the burner down and reduce temperature and pump speed when less energy is required. Clearly you know something that they don't.
Go away and do some reading up on condensing boiler technology and control systems. Come back when you've understood it and we can run a short test. Shall we set the date in 2014 now?
failed again. I'm fed up marking you as it's always a poor score. The outside weather gives the slope and the internal temp sensor (if one fitted. Many internal temp sensors can be fitted and the temps averaged on large buildings) raise or lowers it to suit.
For you:
With heat bank and a weather compensator, a mass of water is heated at the bottom of a heat bank to the temperature what the building requires (the rads). The temp can be anything from 25C to 80C depending on the outside conditions. The temp of the lower mass of water is dictated by the weather compensator, which is near enough the correct temperature that the rads will require.
A load compensating modulating boiler generally goes down to about
5-7kW, any lower than that it cycles on-off. Some super expensive boilers go down to 3kW. As most of the time buildings are up to temp (part load on the heating system) this will be significant cycling in most modulating boilers. These boilers tend to be complex and expensive and have more expensive parts and servicing to go wrong on them.
- With a heat bank the rad circuit(s) can draw-off only 1 kW of heat from the heat bank and no cycling from the boiler. Only when the whole mass of water cools does the boiler come in and re-heat the mass of water in one long efficient no boiler cycling burn.
- The temp of the mass of water is not totally fixed as the temp will drop slightly as the mass of water is cooling. This is insignificant and TRVs trim off local temps. Weather compensating slopes are never fully accurate and may out by +-5%. The slope is a best fit at the best of times. An internal temp sensor (if one fitted), raise or lowers the slope it to suit. Many internal temp sensors can be fitted and the temps averaged on large buildings for greater accuracy..
- A simpler, and cheaper, condensing boiler can be used, similar to any regular heating boiler, that can have the optimum flow through the boiler at all times for greater efficiency and boiler longevity.
- A variable speed Alpha pump can be used on the rad circuits reducing noise electricity consumption.
- If having a heat bank for DHW, then increasing the size to provide: * a cheaper, simpler and more reliable boiler, * a neutral point for all circuits, * weather compensation * elimination of boiler cycling when on part load, which gives far greater boiler longevity on all components. * oversized rads to cope with a condensing boiler giving lower return temperatures. * Variable speed pumps(s) on rad circuits. * instant heat available first things in the mornings. Rads are fully heated with afew minutes.
Now understand this if you can. It is not difficult. If there are parts you are confused about, just accept it as right.
That's good. You weren't invited to in the first place.
We are talking about a simple domestic system here, not a commercial one
So the boiler will be put into a situation where it will cycle frequently when the heatbank temperature is low.
You still haven't suggested a suitable controller.
This is based on a bunch of assumptions which in practice are not the case.
Also, any cycling that does happen will be at the bottom of the modulating range and not full power as in your example. This makes a substantial difference.
This is untrue. The extra complexity is in the firmware of the controlling microprocessor. There are no additional mechanical components
Of course there will be cycling.
You still haven't said whether you are going to maintain the heatbank at the setpoint or allow the temperature to drop to practically room temperature.
How much is "slightly"?
Only if the heat being provided by the water is within the range required and controllable by the TRV. Since you haven't indicated what that will be, this suggestion is guesswork.
5% accuracy on a system for domestic use is pretty good/
It may well be like this or worse on an external box controller such as you describe because the controlled device is an unknown
If you have an external sensor connected to a boiler designed with weather compensation and for use with a nominated sensor, then all the pieces can be matched together as a system and will produce a much better result than can be achieved by throwing bits and pieces together - especially cheap ones as you are suggesting.
By the way, what about that controller?
We are talking about a house, not a commercial building.
Where is this cheaper boiler? Where is the £400 model that you are dying to tell us about?
How are you going to control the flow to optimise it?
A modulating pump is always a good idea to match heat source and load. Better yet if incorporated into the boiler and controlled by its microprocessor.
Which one? I'm still waiting.
How big is this heatstore going to be?
At least 100 litres is needed for the DHW, and 200litres for the space heating. What about the space for these cylinders?
Normally you are squeaking about space saved by combis. Now you are proposing a half baked, unreliable system with huge space requirements.
Only a benefit if there are multiple heat sources.
Except that your suggestion does it poorly in comparison with a full integrated modulating boiler.
It does not eliminate boiler cycling because the damned thing is being switched on and off.
If possible one should always do that with condensing boilers if possible.
How is your system going to cope with heat output required for different radiator design schemes? It is not monitoring the return temperature.
Even better if one is integrated with the boiler and controlled by it.
The same happens with a modulating boiler.
It is better if th control system can monitor the room temperature and back off the heat supply at the right time.
If you dump heat from a store directly into radiators when it has been a cold night and presumably the heatbank temperature is high, you are going to get huge overshoot and waste of heat.
I am not and have never been confused.
Perhaps you would like to answer the questions that you have been avoiding.
So, basically, in a completely predictable way, you can't come up with a boiler for £400 or an external controller for your harebrain scheme..... Not that it was worth doing in the first place.
How much heat is lost when a modulating condensing boiler cycles? Not much I would have thought, as the heat exchanger probably has low thermal mass and operates at a lower temperature.
Another way of doing it would be to connect the lower half of the heat bank/thermal store in line with a differential bypass valve and 2 port valve in parallel.
Then as the system gets up to temperature and the TRVs close, the thermal store would take the excess heat. When that reaches temperature and the burner switches off, the 2 port valve would open to release the heat back into the system.
You are the one who introduced the notion of a simpl, cheap boiler. Until then, the boiler under discussion was the WB modulating model that I mentioned.
You then introduced the notion of an inappropriately applied weather controller. The Danfoss Randall BEM5000 was mentioned but is not really designed for your application, so goodness knows what it would do. Presumably you would advocate splasjing out the money just to find out....
So... Where is this £400 boiler and where is the controller to go with it?
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